This patent relates to catalysts supported on a foraminous carrier and methods for preparing such catalysts using stabilized aqueous compositions. In particular, this patent relates to aqueous compositions containing catalytically-active metal components and substantially water soluble acidic components and to the catalysts prepared using such aqueous compositions for impregnating foraminous carriers. It is desirable to convert heavy hydrocarbons, such as those having a boiling point above about 1000° F., into lighter, and more valuable, hydrocarbons. It is also desirable to treat hydrocarbon feedstocks, particularly petroleum residues, also known as resid feedstocks, in order to carry out, for example, hydrodesulfurization (HDS), hydrodenitrogenation (HDN), carbon residue reduction (CRR), hydrodemetallation (HDM), including the removal of nickel compounds (HDNi) and vanadium compounds (HDV). The catalysts of the present invention are particularly useful and effective in the hydrodesulfurization, hydrodenitrogenation, hydrodemetallation, etc. of petroleum compositions, especially high-boiling petroleum compositions.
Catalysts comprising at least one Group VIII metal component, at least one Group VIB metal component and a phosphorous component, such components being carried on a foraminous carrier, are known in the art.
It is known that the metals of Group VIB of the periodic table, for example tungsten and molybdenum, and components comprising such metals, for example compounds such as the oxides and sulfides, are active in catalyzing a wide variety of reactions including among others, hydrogenation, dehydrogenation, oxidation, desulfurization, isomerization and cracking. However, catalytic metals and components containing them are, relatively costly and have a relatively small surface area per unit weight, so that they are typically not used without resort to carrier materials. Consequently, these catalytically active metals or components are usually applied in a diluted form to the surface of a foraminous support material. The foraminous support material is usually of a low order of activity when compared to the catalytically-active components, or such carriers may even be catalytically completely inactive.
Furthermore, it is known that certain metal-containing components of Group VIII of the periodic table of the elements, such as iron, cobalt, and nickel, when used in combination with the Group VIB metal-containing components, result in enhanced catalytic activity. These Group VIII components are sometimes referred to as catalyst “promoters.” However, problems can result when these promoters are attempted to be impregnated into a carrier along with the catalytically active components of Group VIB. Simple and direct impregnation techniques using a mixture of both components typically cannot be employed. For example, a combination of components based on cobalt or nickel salts with molybdenum or tungsten components typically results in unstable solutions, e.g., solutions subject to the formation of precipitates. Impregnation of a carrier using separate solutions comprising components of Group VIB and Group VIII is not an acceptable alternative since that can result in costly, multi-step processes and ineffective or non-uniform metals distribution.
Rather costly and involved processes have been devised in order to obtain a uniform distribution throughout the available surface area of the foraminous catalyst carrier material when using components containing both of the catalytically active metals of Group VIB and Group VIII. It has been the objective of these methods to prepare solutions containing metals of both Group VIB and Group VIII that are sufficiently concentrated and of the requisite stability to allow subsequent uniform impregnation and distribution of the metals throughout and upon the surface area of the carrier. These methods typically include the use of high concentrations of phosphoric acid. Typically, the carrier is impregnated with a dilute solution comprising a phosphorous component, although some applications do not use a phosphorous component, and components of metals of both Group VIB and Group VIII, by applying the solution to a calcined foraminous carrier material, and then drying and calcining the composite to convert the catalytically active material to other forms, particularly to the oxide. However, the use of phosphoric acid, particularly at high concentrations that are required to readily solubilize both of the metal containing components and maintain them in a stable solution, can introduce performance related problems during the use of such catalysts in hydroconversion processes.
Therefore, it would be an advantage to the art to prepare a stable aqueous composition containing metals from both Group VIB and Group VIII suitable for use in producing a finished catalyst having desirable performance characteristics.
Furthermore, as noted, there is increased interest in producing and upgrading lower quality hydrocarbon feeds, such as synthetic crudes and heavy petroleum crude oil fractions. Unfortunately, high concentrations of nitrogen, sulfur, metals and/or high boiling components, for example, asphaltenes and resins, in such lower quality feeds render the same poorly suited for conversion to useful products in conventional petroleum refining operations. In view of such difficulties, lower quality hydrocarbon feeds often are catalytically hydrotreated to obtain materials having greater utility in conventional downstream refining operations. Catalytic hydrotreating or hydroconversion involves contacting such a feed with hydrogen at elevated temperature and pressure in the presence of suitable catalysts. As a result of such processing, sulfur and nitrogen in the feed are converted largely to hydrogen sulfide and ammonia which are easily removed. Aromatics saturation and cracking of larger molecules often take place to convert high boiling feed components to lower boiling components. Metals content of the feed decreases as a result of deposition of metals on the hydrotreating catalyst.
As can be appreciated, satisfactory operation in processing feeds containing high levels of impurities under severe process conditions places increased demands on the catalyst to be employed as the same must exhibit not only high activity in the presence of impurities and under severe conditions, but also stability and high activity maintenance during the time that it is in use. Catalysts containing a Group VIB metal component, such as a molybdenum and/or tungsten component, promoted by a nickel and/or cobalt component and supported on a porous refractory inorganic oxide are well known and widely used in conventional hydrotreating processes; however, the same often are somewhat lacking in stability and activity maintenance under severe conditions.
It is known that preparation of hydrotreating catalysts containing Group VIB and Group VIII metal components supported on a porous refractory inorganic oxide can be improved through the use of phosphoric acid impregnating solutions of precursors to the Group VIB and Group VIII metal components or the use of phosphoric acid as an impregnation aid for the metal precursors. Thus, Pessimisis, U.S. Pat. No. 3,232,887 discloses stabilization of Group VIB and Group VIII metal-containing solutions through the use of water-soluble acids. According to the patentee, in column 3, lines 6-11, “in its broadest aspect the invention comprises the preparation of stabilized aqueous solutions which comprise an aqueous solvent having dissolved therein catalytically active compounds containing at least one element from Group VIB of the periodic table and one element from Group VIII.” Inorganic oxyacids of phosphorus are included among the disclosed stabilizers, and the examples of Pessimisis illustrate preparation of various cobalt-molybdenum, nickel-molybdenum, and nickel-tungsten catalysts using phosphorus and other acids as stabilizers. Hydrodesulfurization results with certain of the cobalt-molybdenum catalysts are presented, and the patentee suggests that the use of the stabilized solutions may lead to improved hydrodesulfurization activity in some instances.
Similarly, Colgan et al., U.S. Pat. No. 3,287,280 discloses the use of phosphoric acid as an impregnation aid in preparation of nickel-molybdenum catalysts and that such use can result in catalysts having improved hydrodesulfurization activity.
Colgan et al., U.S. Pat. No. 3,840,472 disclose catalysts prepared by impregnation of an alumina support with stabilized solutions of molybdic oxide and certain cobalt or nickel salts dissolved in aqueous phosphoric acid although the patentees suggest that the presence of certain amounts of a phosphorus component in the ultimate catalyst may harm performance; see column 2, lines 23-28.
Simpson, U.S. Pat. No. 4,255,282 discloses hydrotreating catalysts comprising molybdenum, nickel, and phosphorus components and a gamma-alumina support, such catalysts being prepared by a method that involves a precalcination of the gamma-alumina at a temperature greater than 746° C. With respect to the phosphorus component, Simpson teaches that the same often has been included in hydrotreating catalysts to increase catalyst acidity and thereby improve activity.
While the patents and publication discussed above disclose that the use of phosphoric acid in the preparation of hydrotreating catalysts containing Group VIB and Group VIII metal components is beneficial to the preparations, reported effects on catalytic activity and performance vary significantly. For example, the general statement in Simpson, U.S. Pat. No. 4,255,282 regarding use of a phosphorus component to increase acidity and thereby improve activity, is contrary to the teaching of Colgan, U.S. Pat. No. 3,840,472 that use of phosphoric acid in improper amounts can adversely affect catalyst activity and strength.
Other patents relating to hydroconversion or hydrotreating processes disclose various catalysts, their method of preparation as well as their use in such processes. For example, Simpson et al., U.S. Pat. No. 4,500,424 and its divisional patent, U.S. Pat. No. 4,818,743 are directed to hydrocarbon conversion catalysts containing at least one Group VIB metal component, at least one Group VIII metal component, and a phosphorus component on a porous refractory oxide having a defined and narrow pore size distribution. The catalyst is said to be useful for promoting various hydrocarbon conversion reactions, particularly hydrodesulfurization. Similarly, Nelson et al., U.S. Pat. No. 5,545,602 is directed to hydrotreatment of heavy hydrocarbons to increase content of components boiling below 1000° F. by contact with Group VIII non-noble metal oxide and Group VIB metal oxide on alumina having specific and defined surface area and pore size distribution. This patent also teaches, at column 9, lines 36-37, to avoid adding phosphorous containing components during catalyst preparation because “Presence of phosphorous undesirably contributes to sediment formation.” In furtherance of this teaching it is suggested, at lines 54-57, that impregnating solutions may be stabilized with H2O2 so that solutions stabilized with H3PO4 not be used. See also Dai et al., U.S. Pat. Nos. 5,397,956 and 5,498,586 similarly directed to defined carrier properties for improved hydroconversion catalysts.
Plantenga, et al., U.S. Pat. No. 6,566,296 relates to a process for preparing a catalyst composition wherein at least one Group VIII non-noble metal component and at least two Group VIB metal components are combined and reacted in the presence of a protic liquid, e.g., water, and an organic oxygen-containing additive, e.g., diethyleneglycol, is added. The resulting composition is isolated and dried, and, while calcining is an option that results in removal of the oxygen-containing additive, the examples are directed to dried and crushed catalyst particles.
Notwithstanding the diverse teachings of the above patents and publication in respect of the preparation of hydrotreating catalysts, there is a continuing need for development of improved catalysts.